Filtering techniques

Claim 1

A system for filtering digital signals representative of color in pixels of multidimensional graphic information comprising: means for receiving a digital signal representation of color in pixels, said received digital signal comprising chromatically multicolor, multifeature graphic information; means for recognizing an array of pixels circumjacent to each pixel; treating means, responsive to the digital graphic information in the array of pixels circumjacent to each pixel, for treating that pixel according to a methodology which selectively filters the digital signal representation of the pixel to produce selectively filtered digital signals by a first digital filtering process which includes a chromatic color dependent filtering process selectively causing the digital signal representation to be filtered by a second digital filtering process and for removing random dots; means responsive to the filtered digital signals for creating a representation of said multifeature graphic information as filtered more accurately representative of said multifeature graphic information than the received digital signal; said treating means chromatic color dependent filtering process including means for processing colors (cin) in each pixel of said digital graphic information by: determining in a first step (42) if a pixel color (Cin) is a background color of a halftone dot color; determining in a second step (44), in response to a positive determination in said first step (42) if a pixel color is a predetermined "color to keep" and a sum of a histogram of pixels with a histogram of pixels of background colors exceeds a first threshold (T5); determining in a third step (50) reached by a negative determination in said second step (44) if a sum of a histogram of pixels with a histogram of pixels of background colors exceeds a second threshold (T1) and a histogram of pixels of halftone dots, exceeds a third threshold (T2); determining in a fourth step (54) in response to a negative determination in said first step or said third step if a pixel is a background color and a sum of a histogram of pixels of background color and a histogram of pixels of a solid color exceeds a fourth threshold (T3) and a histogram of pixels of a background color exceed a fifth threshold (T4); generating (46, 58) an unchanged output pixel in response to a positive determination in said second and fourth determining steps; generating (52) an output pixel of a background color corresponding to a background color causing a positive determination in said third step; and generating (62) an output pixel corresponding to a plurality color in said array in response to a negative determination in said fourth step; said treating means second digit of filtering process including means for processing each pixel of said digital graphing information by: determining in a second first step (72) if a histogram of pixels of a color of halftone dots exceeds a second first threshold (T1) and a sum of a histogram of pixels of a color of halftone dots and a histogram of background colors exceeds a second threshold (T2); repeating (76) said first step for all halftone dot colors; generating (74, 78) an output pixel of a color corresponding to a halftone dot color in response to a positive determination in said second first step; and generating (80) an unchanged output pixel in response to a negative determination in said second first step; said treating step further including the steps of: defining (92) an error color for pixels within an area; converting (96) each pixel of error color in said area to a replacement color.

Claim 2

A system for filtering digital signals representative of color in pixels of multidimensional graphic information comprising: means for receiving a digital signal representation of color in pixels, said received digital signal comprising chromatically multicolor, multifeature graphic information; means for recognizing an array of pixels circumjacent to each pixel; treating means, responsive to the digital graphic information in the array of pixels circumjacent to each pixel, for treating that pixel according to a methodology which selectively filters the digital signal representation of the pixel to produce selectively filtered digital signals by a first digital filtering process which includes a chromatic color dependent filtering process selectively causing the digital signal representation to be filtered by a second digital filtering process and for removing random dots; means responsive to the filtered digital signals for creating a representation of said multifeature graphic information as filtered more accurately representative of said multifeature graphic information than the received digital signal; said treating means chromatic color dependent filtering process including means for processing colors (cin) in each pixel of said digital graphic information by: determining in a first step (42) if a pixel color (Cin) is a background color of a halftone dot color; determining in a second step (44), in response to a positive determination in said first step (42) if a pixel color is a predetermined "color to keep" and a sum of a histogram of pixels with a histogram of pixels of background colors exceeds a first threshold (T5); determining in a third step (50) reached by a negative determination in said second step (44) if a sum of a histogram of pixels with a histogram of pixels of background colors exceeds a second threshold (T1) and a histogram of pixels of halftone dots, exceeds a third threshold (T2); determining in a fourth step (54) in response to a negative determination in said first step or said third step if a pixel is a background color and a sum of a histogram of pixels of background color and a histogram of pixels of a solid color exceeds a fourth threshold (T3) and a histogram of pixels of a background color exceed a fifth threshold (T4); generating (46, 58) an unchanged output pixel in response to a positive determination in said second and fourth determining steps; generating (52) an output pixel of a background color corresponding to a background color causing a positive determination in said third step; and generating (62) an output pixel corresponding to a plurality color in said array in response to a negative determination in said fourth step; said treating means second digit of filtering process including means for processing each pixel of said digital graphing information by: determining in a second first step (72) if a histogram of pixels of a color of halftone dots exceeds a second first threshold (T1) and a sum of a histogram of pixels of a color of halftone dots and a histogram of background colors exceeds a second threshold (T2); repeating (76) said first step for all halftone dot colors; generating (74, 78) an output pixel of a color corresponding to a halftone dot color in response to a positive determination in said second first step; and generating (80) an unchanged output pixel in response to a negative determination in said second first step; said treating step further including the steps of: defining (92) an error color for pixels within an area; converting (96) each pixel of error color in said area to a replacement color.